Two trains pass each other on parallel lines Each train is $100$ m long. When they are going in the same direction the faster one takes $60$ seconds to pass the other completely. If they are going in opposite directions they pass each other completely in $10$ seconds. Find the speed of the slower train in km/hr

Using the relative speed formula, the relative speed in the same direction is (100+100)/60 = 10/3 m/s, and in opposite directions is (100+100)/10 = 20 m/s. Solving the equations Sf - Ss = 10/3 and Sf + Ss = 20 gives the slower speed Ss = 25/3 m/s. Converting this to km/hr yields (25/3) * (18/5) = 30 km/hr.

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